At what temperature was 1 kg of water if 600 grams of firewood were burned for complete

At what temperature was 1 kg of water if 600 grams of firewood were burned for complete evaporation at 100 degrees. Efficiency = 40%

Data: m1 (water) = 1 kg; m2 (wood) = 600 g = 0.6 kg; η (efficiency) = 40% = 0.4.

Reference values: tboil = 100 ºС; q (beats heat of combustion) = 1 * 10 ^ 7 J / kg; C (specific heat capacity) = 4200 J / (kg * K); L (beats heat of steam) = 2.3 * 10 ^ 6 J / kg.

η = (С * m1 * (tboil – tн) + L * m1) / (q * m2).

С * m1 * (tboil – tн) + L * m1 = η * q * m2.

tboil – tн = (η * q * m2 – L * m1) / (С * m1).

tн = tboil – ((η * q * m2 – L * m1) / (C * m1)) = 100 – ((0.4 * 1 * 10 ^ 7 * 0.6 – 2.3 * 10 ^ 6 * 1) / (4200 * 1)) = 76.19 ºС.